The invention resides in a motor brake for an internal combustion engine which includes an operating mechanism for an exhaust valve of the engine.
For the deceleration of a vehicle operated by an internal combustion engine often motor brakes are used in addition to the normal vehicle brakes. To this end, the exhaust gas system of the internal combustion engine includes a throttle valve by means of which the exhaust gas backpressure in the exhaust system can be increased when desired. The increased exhaust gas back pressure is effective, by way of the open exhaust valves on the pistons of the engine so as to brake the engine.
In order to achieve a good braking effect, the operating mechanism for the exhaust valves of an internal combustion engine may open the valves at times different from those provided by the camshaft of the engine. During braking operation, the exhaust valves are kept at least partially open for periods adapted to the braking operation, such that communication between the exhaust system and the cylinders is provided which generates in the cylinders a high backpressure effective on the pistons so as to provide for engine braking.
DE 39 22 884 discloses a motor brake for an engine with a camshaft disposed below the hydraulic valve lifters and push rods extending upwardly from the valve lifters. The hydraulic valve lifters include a central bore in which a hydraulic piston is disposed by way of which the exhaust valve can be opened when, during braking operation, hydraulic fluid under pressure is supplied to the valve lifters.
However, in this arrangement, it is disadvantageous that, upon lifting of the valve lifter by the camshaft the hydraulic piston and, together therewith the push rod is also raised unless expensive counter measures are employed. The uncoupling of the camshaft-based opening of the valve from its opening for the purpose of motor braking is difficult. During motor braking operation, the hydraulic pressure effective on the hydraulic piston is also effective—in opposite direction—on the lifter which, therefore is biased against the camshaft resulting in wear of the camshaft.
It is the object of the present invention to provide a motor brake with an operating arrangement for an exhaust valve which can be actuated in a simple manner with respect to the different operating parameters and which results only in relatively little mechanical loads.